In a shabby, concrete arena of broken plastic seats, shrill pop music blasts out as a ringmaster in a purple suit uses a metal rod to strike a tiger balancing on top of a large plastic ball and moving in alarming jolts across the ring's dirty floor. The animal snarls half-heartedly as three other tigers stare impassively from a row of stools. Then, one after another, they go through a tired routine of stunts, jumping through hoops and sitting to order before being chased out of the ring into cages below.

There follows 25 minutes or so of tamer, but equally questionable, circus entertainment, such as chained bears and monkeys riding bicycles and a goat walking a high wire with a monkey clinging to its back, met with a smattering of applause from a pitifully small audience.

This sad spectacle plays out at 2.30pm every day at the Xiongsen Bear and Tiger Mountain Village, in Guilin, southwestern China, and - in the three decades since the park opened - has never been less popular or drawn smaller audiences than the rows of near-deserted seats suggest is the case now. This used to be one of the city's premier tourist attractions, but on a Thursday in March, when we visited, just three people attended the show. Two days later, there was a weekend afternoon audience of fewer than 30.

The venue looks for all the world like an outdated wildlife park on the brink of closure, but employees say the park will soon be moved by its tycoon owner, Zhou Weisen, to a site 8km away that is three times the size. What's more, rather than declining in line with the falling visitor numbers, the tiger numbers are booming and the park now claims to be home to the world's biggest captive population: more than 1,800 animals. According to the most recent data, globally only 3,890 tigers exist in the wild.

If it relied on the 40 yuan (HK$48) admission fee from its sprinkling of guests, the park could not feed more than a fraction of its animals and could never break even. But the Xiongsen Bear and Tiger Mountain Village doesn't profit from entertainment. The grim circus is mere window dressing to disguise the park's true purpose - the breeding of big cats to supply a highly profitable trade in tiger bone wine, which is brewed in a vast underground factory some 300km away, in the Guangxi countryside.

When the tigers of Xiongsen die - be it from old age, illness or fights with other cats - they are taken to the factory, in Zhou's hometown, Pingnan, where their skeletons are steeped in huge vats of rice wine for up to eight years, park insiders say. The liquid is bottled and sold for between 320 yuan and 4,000 yuan a half litre.

This elixir, customers believe, has medicinal powers (see below), and China's rapidly expanding middle class and the advent of online sales have seen its popularity boom in the past decade. China's thirst for the illicit product is apparently so insatiable that existing tiger farms are expanding, while new farms are being set up in neighbouring countries such as Laos and Vietnam to feed the demand.

Tiger wine from Xiongsen is the best in China and a lot of our business comes over the internet now

Post Magazinefirst exposed the practice in 2007, when the Guilin park attracted hundreds of visitors a day and featured a live feeding show, in which calves were put into tiger enclosures to be mauled to death and eaten in front of whooping family audiences. Then, tiger bone wine was sold openly for 450 to 900 yuan a bottle in a shop that had a tiger skeleton on display in a glass case. In the park's restaurant, waitresses handed out menus that included lion meat for 380 yuan a dish, bear paws for 7,200 yuan and "big king" - a euphemism for tiger - meat for 480 yuan a dish.

The controversy over the article and the many follow-up features by other publications forced the shop and restaurant to close and led to a sharp fall in visitor numbers. What that exposure did not do, however, was dampen the demand for tiger bone wine, which today appears stronger than ever, with the Guilin facility - along with another government-approved tiger park in Harbin, in the far north of China, which is home to more than 1,000 cats - feeding a sizeable portion of the market.

Breeding tigers for their body parts is banned under the Convention on International Trade in Endangered Species (Cites), to which China is a signatory - but Beijing has granted an exemption to breeders of captive tigers, who argue that their farms reduce poaching of wild animals. That is a claim fiercely disputed by conservation groups, who say that by driving demand, tiger farms encourage poaching in countries such as India, where the cost of killing a cat in the wild is far lower than the price of raising a captive beast.

The controversy has been highlighted by state broadcaster CCTV, which carried a critical report on Xiongsen in 2014. As a result, the park is exceptionally wary of the few visitors it receives, particularly foreigners. We were warned not to take pictures as soon as we arrived at the ticket office and are shadowed by security guards with walkie-talkies throughout our visit.

It is only during brief moments when we are able to give our unofficial minders the slip that we can shoot pictures and video of some of the wretched, bored and neglected-looking tigers in the park. When we ask about the painfully thin condition of some of the animals, one guard following us shakes his head and says, "There are so many of them here now it's hard to feed them all and there isn't enough food to go around."

At afternoon feeding time, a shockingly emaciated tiger - the bones of its back and hind legs protruding sharply beneath its fur - tries to eat one or two chunks of pork thrown into its enclosure before being chased away by healthier animals.

Out of sight of the public areas of the park, we find row upon row of rusting cages, engulfed with weeds, in which tigers are kept in ones and twos.

Getting a glimpse of the lucrative trade these tigers generate takes a half-day drive across rural Guizhou, to Pingnan, where, eight years ago, Zhou opened a five-star hotel with a shop attached, in which tiger bone wine is openly sold. A 500ml bottle of wine from a vat in the nearby factory that contained tiger bone and penis is on offer for 4,000 yuan. Wine containing bear paw as well as tiger bone costs 1,000 yuan a bottle.

Although labelled as a tonic drink, with no mention of its feline ingredients, the wine is ostentatiously presented in tiger-shaped bottles and staff at both the shop and restaurant assure us it is made with genuine bone from the Xiongsen park. Behind the counter, boxes of tiger wine are piled almost to the ceiling, ready to be shipped to customers across China.

"Tiger wine from Xiongsen is the best in China and a lot of our business comes over the internet now," the shop assistant says, proudly.

Xiongsen's tiger bone wine has its own page on Alibaba, the world's biggest online trading site, where buyers are given an assurance that what they see are genuine tiger bone products from the Guilin park. Alibaba is also owner of the South China Morning Post.

Inside the hotel, diners are handed menus listing a range of tiger wines to accompany meals. Zhou's face features on the labels of some bottles. Here, the price of a 500ml bottle of six-year-old tiger wine from the factory is 1,300 yuan.

Each dead tiger from Xiongsen can produce wine with a retail value of hundreds of thousands of dollars - but what happens to the rest of the cat after its bones are put in the Pingnan vats is shrouded in mystery. The factory is heavily guarded and only staff are allowed past the gates.

After being briefed on our findings, Shruti Suresh, a wildlife campaigner with the London-based Environmental Investigation Agency (EIA), says they support her organisation's belief that the tiger bone wine trade is growing at a rapid pace.

"It seems predominantly the market is a high-end luxury market catering to big hotels, big banquets. It is a luxury product. If it is available online you can order it from anywhere and see if it makes it to you without being seized on the way," she says.

"It is interesting that the Xiongsen park is so overgrown and that there are so few people there because often the argument facilities like this put forward is that it has a conservation impact or that it raises awareness about wild tigers. But this has nothing to do with conservation. They are basically factories like any other industry and the main objective is profit."

The EIA has uncovered evidence that tiger farms are being set up in Southeast Asia, including one with 500 animals in Laos, in a special economic zone near the Chinese border.

"We found a tiger breeding facility in that zone which was planning to expand its operations primarily to manufacture tiger bone wine on a commercial scale for export to China," Suresh says.

"Tigers do breed at a high rate and the number in China could triple in no time if action is not taken quickly to stop the breeding," she says. "If China is serious about tiger conservation, they could invite a group of technical experts from conservation, animal rescue and welfare organisations to assist the government with a policy to phase out commercial facilities that keep or breed tigers."

For now, however - as more tigers than ever are born to suffer wretched, short lives - China's thirst for the wine made from their bones shows no signs of being quenched.

What tiger bone wine tastes like, and how it makes you feel

Tiger bone wine tastes like a mixture of cough medicine and three-star Metaxa brandy, and the moment it passes your lips you can sense the thumping hangover this foul liquid will leave in its wake.

If, however, you believe in the extremes of traditional Chinese medicine, this evil-smelling concoction will cure rheumatism and back pain, prolong life and give you the strength and sexual prowess of a tiger.

I bought a 500ml bottle of year-old tiger bone wine made, I was assured by the saleswoman, from the skeleton of a Xiongsen tiger and drank it in a Guilin restaurant with a friend and colleague, Mr Jiang, a retired academic. The most appealing, or rather the only appealing, aspect of it was the bottle - in the shape of a benign, Disney-fied cuddly tiger: an image that was a world away from the tormented, starving wretches we saw earlier pacing rusty, neglected cages inside the park.

Lift off the head of what, from a distance, looks more like a child's toy than a bottle, and beneath is a plastic screw stopper. The wine is surprisingly thick and brown. Into thimble-sized glasses we poured shots, which, as custom dictates, must be downed in one go.

I had expected a pure liquid but, reading the label, Jiang explained it was mixed with herbs and even had some snake in it, giving it the dark brown colour.

The first glass was undoubtedly the worst. While, at 38 per cent proof it is not as strong as many liquors, its sweetness and thick texture were hard to stomach. Like any bad holiday drink, however, it mysteriously improved in quality with each glass.

"Of course the medicinal claims made about it are total nonsense," Jiang declared loftily, as he raised his glass for a fifth toast. "But there are 1.3 billion people in China and if only half of us believe it, it makes for very good business."

I woke the next morning like a tiger with a sore head, in possession of a roaring hangover and a collection of previously unknown bodily aches. The wine's supposed curative qualities appeared to have worked in reverse.

However, Jiang, who had taken the bottle home with him, had turned from cynic to believer overnight.

"I felt very sprightly when I got home and my wife was very happy," he told me in an excited phone call. "Maybe there is something to what they say after all."